LA-4 Help Thread!

[gar381]

I'm using Hairballs VU meters in mine

http://hairballaudio.com/shop/product_info.php?cPath=25&products_id=40

these work VERY well in LA4s.

GARY

 

[helterbelter]

The guy at the store said I only needed a 25 watt iron. I hope he wasn't lying.

15 watts is enough. More than 30 would be overkill. But in case you like to do the electronics DIY, I suggest that you buy a soldering station with a ground connection to the tip later. Especially when using ESD sensitive components this will be better. But the parts on the LA4 will surely stand the iron that you have, no need to buy a station right now.
Though, use sockets for the opamps (TL074's) and don't place the BD transistors before you've soldered everything else.

Enjoy !

 

[Piotr]

Hi to all !!!

A simple but informative question: what should be the voltage rating for all the ceramics in the project ? Thanks, Piotr.

 

[helterbelter]

ceramic caps ?

Doesn't matter.
Normal ceramic caps can stand 100 volts, so there's no need to look into that.

 

[Piotr]

Thanks HelterBelter !

I'm also in trouble finding the TL074CP, I've found the ACN, BCN, CN types. Is the CN type ok ?

I've checked the TI specs...and want to be sure. (http://focus.ti.com/general/docs/lit/getliterature.tsp?genericPartNumber=tl074&fileType=pdf)

Thanks !!!

 

[Matthew Jacobs]

Hi Piotr

I don't think it matters at all which TL074 you use.

I used the TL074CNE4 cause that's what I found on Farnell.

As long as the pinout is the same, shouldn't matter. Other than that just make sure you are happy with the specs from the data sheet such as slew rate and bandwidth.

BTW, this compressor is awesome. Almost finished mine (just waiting for Sifam meters from Canford) but already tried it on a live rig last week. Excellent on bass, just made it "pop" out, Ac Gtr, Snare. Works on vocals but only for aggressive rock IMHO.

All in all this is a compressor with a lot of character (TL074, Iron, etc) and you can't really go wrong with whatever component you select. I wish you all the best in your build and hope you enjoy it when finished.

A Plus

J

 

[Piotr]

Hi again,

I'm having trouble in finding the trimmers in 10mm spacing. I've already twisted and bended trimmer legs so that's one option... But if some of you know of Farnell available suitable trimmers then great !!! Thanks for your help ! Piotr.

 

[Piotr]

Hi all !
correcting my previous post, seems like the 3386G series from Bourns is OK...

 

[Piotr]

Hi....me again !

I am gathering the parts to build a stereo unit and I have one more question (learning all this results in a lot of questions !!!)

To put it simply is one power supply on one of the boards sufficient for two boards ?

The current draw seems to be 160mA per stereo unit and according to the pcb layout one "2 X 18V DC" is to be connected to the 2 X 18V DC input in the upper part of the board, and the second, labelled "2 X 18V supply" should provide power to the second LA-4 board.

Am I correct or just plain stupid ?

If I'm correct then is the 15 VA toroid sufficient in this double board application ? The toroid is rated 7,5 VA per secondary so 7,5/18=0,416 A. Seems correct and sufficient...but I always prefer to double check...

Thanks again !!! Piotr.

 

[MrZpliff]

Hi....me again !

I am gathering the parts to build a stereo unit and I have one more question (learning all this results in a lot of questions !!!)

To put it simply is one power supply on one of the boards sufficient for two boards ?

The current draw seems to be 160mA per stereo unit and according to the pcb layout one "2 X 18V DC" is to be connected to the 2 X 18V DC input in the upper part of the board, and the second, labelled "2 X 18V supply" should provide power to the second LA-4 board.

Am I correct or just plain stupid ?

If I'm correct then is the 15 VA toroid sufficient in this double board application ? The toroid is rated 7,5 VA per secondary so 7,5/18=0,416 A. Seems correct and sufficient...but I always prefer to double check...

Thanks again !!! Piotr.

Seems ok to me. It says 18V, 15VA in the BOM also.

 

[helterbelter]

Yep, all is correct.

 

[Rybow]

So I think I made a big mistake. I believe I just bought all carbon film resistors for this thing, and I am not sure if they will let me take them back. Grrrr. Is there a big issue here? I am still going to try to exchange them for metal film ones. Transformers might be tough to track down though. I can only find Hammond trannies in this city.

Parts are coming along though! I can't wait to get started on this puppy.

 

[dustbro]

Is there a big issue here?

You only really need metal film where it says 1% on the board.
good luck

 

[Rybow]

Sweet! Thanks very much!

 

[helterbelter]

Transformers might be tough to track down though. I can only find Hammond trannies in this city.

Well, maybe not Vancouver, but in Canada, Bryan has got nice OEP's which I used for my LA4's as well.

http://diypartssupply.com/index.php?main_page=product_info&cPath=4&products_id=4

 

[Rybow]

[/quote]

Well, maybe not Vancouver, but in Canada, Bryan has got nice OEP's which I used for my LA4's as well.

http://diypartssupply.com/index.php?main_page=product_info&cPath=4&products_id=4
[/quote]

Thanks for that link helterbelter. That makes things much easier.

When I tried to track down the power supply, the guy at the store asked me what amperage I needed it to be. I said "?". Now I have been pouring over the internet trying to figure out how I can calculate the amperage of this puppy, but I got nothing. I looked in the manual to see if there is a current spec, but I couldn't find it. One of the above posts states 160mA per stereo unit. Since I am building a mono unit, what am I looking for? So I can learn a little bit, if someone can just give me a hint or two as to where I look to figure out the current draw, that would be sweet.

I picked up a book to try and learn all this stuff called Practical Electronics. It may as well have been written in Russian. Still on the hunt. Looking at Art of Linear Electronics, and Teach yourself electricity and electronics. The Art of electronics is a little out of my price range. Trying to avoid electronics for dummies. Thanks for all the help on this one!

 

[Luny Tune]

I've got 230V/50VA transformers in my dual ones. If you're on 110V you need to compensate for higher current.

 

[Rob Flinn]

I've got 230V/50VA transformers in my dual ones. If you're on 110V you need to compensate for higher current.

30VA is ample & the VA rating would be the same whether you are on 115v or 230v,  since it is V x I & is a power rating.

 

[Rybow]

Alrighty. So I think I found a power transformer. When wired in parallel, it will supply the 117 VAC needed for my north american power. It will supply 18 V at 0.84 amps. Good times? or too much. The full spec is 15VA, series 36V @ 0.42A, Parallel 18V @ 0.84A, dual secondary.

 

[MrZpliff]

Alrighty. So I think I found a power transformer. When wired in parallel, it will supply the 117 VAC needed for my north american power. It will supply 18 V at 0.84 amps. Good times? or too much. The full spec is 15VA, series 36V @ 0.42A, Parallel 18V @ 0.84A, dual secondary.

The power/current rating can not be too high. That's only how much it can deliever at maxium load. As long as the transformer can deliver more current (or power) than the circuit will actually use it's fine... But if it's too small it will get hot or break or burn or something. It can be too physically bee to big as higher rating usually means larger.

Voltage can of course be to high !

In this case I´d say: go for 18V, 30 VA too be shure.